16 February 2011

Are cows magnetic sensors? Re-examining northern alignment

ResearchBlogging.orgA couple of years ago, a paper by Begall and colleagues made a big splash by claiming that cows could detect, and align to, earth’s magnetic field. This report took on a life of its own. I heard it within the last week on one of the science podcasts I listen to (though I can’t remember which one).

This paper got attention not only because this was an unusual claim, but for the way that they determined this. Instead of generating their own data, they looked at pictures of cows in Google Earth.

We know that some animals have a magnetic sense; this is pretty much beyond question at this point (for birds, see Ed Yong’s posts here; here; here). But particularly in mammals, we’re not quite sure how they do it.

It’s very unsatisfying when you don’t have a mechanism for a phenomenon. This is why “And how does that work?” is such an incredibly powerful question to ask people selling expensive water that they claim benefits health, holographic bracelets that improve strength, and so on. If you can’t find a plausible mechanism, you don’t have a good understanding of what’s going on.

Hert and colleagues set out to try to replicate the earlier findings, again using Google Earth images.

They found cows were oriented randomly with respect to direction.

And I should add that they also had two sets of data, that were analyzed separately. So it’s not as though this is a one off fluke; maybe a two-off fluke, but not one time happenstance.

Nature abhors a contradiction. How can these two dramatically different results be reconciled?

One possibility is that this study measured the directions of individual cows. The earlier project measured the direction of herds. Begall and colleagues argued:

Cattle of the same heard might not orient independently of each other, and we therefore calculated a single mean vector per pasture that was used in further analysis(.)

There are other subtle differences between the two studies. Begall and company measure to the nearest 5°. Hert and company apparently measured more precisely, but added 4° random “jitter” to the measurements “to account for imprecision in the measurements”.

It’s also important to note that this study doesn’t mean the earlier one was completely wrong. It presented data from three species, and the cows actually showed the weakest trend to northern orientation of the three. The apparent preferences for a northern orientation in deer were much stronger.

The good news in all this is that because these data are fairly easy to get (you don’t have to take all those aerial photos yourself!), the fact of the matter should come clear fairly quickly as more people try to find the effect.

The bad news is that if it turns out that there’s nothing to it, unfortunately, there will be a lot of “Did you know cows orient to the north?” out there for a long time...


Begall S, Cerveny J, Neef J, Vojtech O, Burda H. 2008. Magnetic alignment in grazing and resting cattle and deer Proceedings of the National Academy of Sciences 105(36): 13451-13455. DOI: 10.1073/pnas.0803650105

Hert J, Jelinek L, Pekarek L, Pavlicek A. 2011. No alignment of cattle along geomagnetic field lines found Journal of Comparative Physiology A. DOI: 10.1007/s00359-011-0628-7

Photo by clarissa~ on Flickr; used under a Creative Commons license.


Bjørn Østman said...

Which other explanations for cow alignment has been given?

Something to do with the sun, maybe? What times of the day are the Google images taken?

Unknown said...

I have always correlated herd direction with wind direction -- and, where you have strong prevailing winds, you will get synchronicity.

Africa Gomez said...

There has been a recent paper on foxes on the same topic:

Covered in Not Exactly Rocket science: